Solar thermal firms are bamboozling householders with high pressure sales tactics and misleading financial statistics, an undercover investigation by a consumer group has found.
Which? condemned most of the companies it came across as "cowboys" and cautioned that the Government would have to clean up the taxpayer-backed industry, vital for the battle against climate change, unless it improved its performance.
The consumer group launched its investigation after a rise in complaints about solar thermal firms. Undercover researchers rented a house in southern England and invited firms to quote for installing solar thermal systems, which use sunlight to heat tap water, as opposed to solar PV systems, which generate electricity - and which were not involved in the Which? exercise.
Of the 10 that exaggerated the financial savings that could be made, the double-glazing giant Everest subsequently admitted that its representative had made false claims – that its system could save 30 times more money than was possible.
Another firm, Ideal Solar Energy, wrongly claimed a solar scheme could halve gas bills and grossly misquoted energy supply statistics from the energy regulator Ofgem.
Which? said: "While these two companies concerned us the most, we received poor service and exaggerated claims of performance from nearly all 14 firms."
Its chief executive, Peter Vicary-Smith, said: "Most of the firms in our investigation behaved like true cowboys – they promised huge savings that bore no relation to reality, and some really piled pressure on the homeowner to sign up immediately or risk losing a one-off 'special offer'."
He added: "The solar industry is too important to our long-term energy needs for things to drag on like this."
Neil McLoughlin, a trading standards officer who saw undercover footage of the Everest sales visit, said the precise nature of the quotation made the claim even more misleading and suggested the Everest may have broken the law on sales tactics by offering thousands of pounds off the price for making a decision "on the spot".
After being informed of the "sting", Everest said: "We're disappointed that our representative failed to use the sales support documentation provided and made claims he knew to be false."
In addition to boasting it could halve gas bills, Ideal successively dropped its originally quote of £8,690 to £5,860 and made a "pushy" phone call to the householder. It also misquoted statistics from energy regulator Ofgem about the proportion of a gas bill that goes on heating.
Ideal later defended its pitch, saying: "Like all retailers, we offer limited promotions on a selective basis" and added it instructed its sales agents not to specify savings to hot water bills.
Just one company, Southern Solar, was found to be helpful and provide sensible advice.
Last year, the OFT received 1,000 complaints about the solar panel industry – high for an industry with fewer than 100,000 installations in UK homes.
The Renewable Energy Association, a trade body which runs an assurance scheme for solar installers, said it was concerned by the report. A spokesman said: "We will be contacting Which? to follow up on their investigation, and take any action necessary against any of the companies which are members of our scheme."